I didn't want to hijack the Wrestling and stuff thread.  I've been considering taking some lessons in brazilian jujitsu, since a Gracie place just opened in my town. I have no intention of competing; it would be really just to: (1) stay in shape (2) learn some stuff to help prevent getting killed in a fight; and (3) be a bit more social.

Of course, I don't want be outed. I've been on T for 3+ years, and had top surgery, but not bottom surgery. I pass very well, but my main concern is how to deal with showers / locker rooms and whether I might be found out given the extremely physical nature of the sport.

If any of you guys have done this, please chime in with your experience.

I started practicing martial arts for the same reasons as you about two months ago. My dojo does a rotation of karate, jiu jitsu, and judo. I am pre-T and haven't had any surgeries. I came out to my sensei and the owner of the dojo. They both said they didn't think it would be an issue. I bind and pack daily, and haven't had a single issue yet. I wear compression shorts with cup and packer under my gi. I change in the mens room and no one in my classes knows anything except I'm just another guy.

Tl;dr: I wouldn't be super concerned about it. I know some things will be different from my experience since you're doing MMA, but since you've had top surgery and are on T, I really don't think you'll have any problems. No one showers in my dojo, and never strip naked. Just have fun and learn a lot, martial arts are a blast!!!

I've done BJJ, Kick Boxing and Karate when I was younger.
But it was when I was pre-t and nothing was changed.
I stopped because of transition but here's my advice.

Everywhere I've done mixed martial arts, very few people took their showers at the gym.
Most just took our gi off and left.

When it comes to locker rooms, no reason for anyone to see your junk.
Just come to the gym with shorts and a t-shirt, and throw your gi on top once you get to the gym.
Most guys don't wear a shirt under the gi though, but I doubt anyone will question you about your scars.

Btw your gi WILL come off eventually in a fight. So if you don't want people to see chest scars, keep your tshirt under.
Also make sure your shorts under your gi are well secured. I'm sure you can guess why.

Third, guys wear jockstraps (duh). So as long as you have one on, no one will question what's inside the cup.
Personally, I wouldn't put a packer in there because fighting bjj can get crazy, you'll be rubbing and twisting
all over your partner so the chances of a packer sliding out would be very high.
Your call.

Hope that helps!

I do Judo in girl mode because I'm pre-t and just don't pass well enough to try.

If you've been on T that long and have had top surgery, I doubt anyone will question you.  I also agree with Jayr that you shouldn't pack-- no one needs that thing falling out while you're rolling.

But I'm sure you know, BJJ is not shy about the contact.  Be ready for people to be grabbing around your upper thigh and reaching up for your belt, wrapping their legs around your neck, laying on top of you-- everything.  Be prepared to get sweaty man crotch in your face.  I doubt you'll have any problems passing, but don't shy away from people when they grab you, cuz that's just what it is.

It's a lot of fun.  I love the ground fighting part of Judo.  I originally wanted to do BJJ but couldn't because of the times and prices of the class.